In the current business environment, new manufacturing methods are required to shorten product cycle times and reduce costs in order to remain competitive and provide a level of service which is demanded by customers. Companies, including semiconductor manufacturers, have utilized methodologies, such as lean manufacturing, to achieve these objectives. Range management is a process which utilizes lean manufacturing techniques for managing daily work flow and driving sustained reductions in cycle time, inventory and cost, and for driving gains in output.
Range management systems focus on delivering work-in-progress (WIP) on a known route at a known speed to meet committed customer deliveries on schedule. In a typical range management system, manufacturing is partitioned into a series of flows, where the products in each flow follow similar routes through the fabrication facility. These flows are divided into ranges, and each range may include one or more operations. An operation is where the units (e.g., wafers) of a production lot are actually worked on, and may include, for example: lithography, metrology, overlay, metrology CD, etc. The collection of operations of a range typically sum to one day of cycle time.
The WIP for each customer is typically assigned a given x-factor so that each lot in the line can be moved relative to other lots in a controlled manner. The x-factor is used to define the speed of the flow, and determine how many operations will fit into one day of cycle time. The x-factor is equivalent to cycle-time performance divided by raw processing time, as understood by one skilled in the art. The goal is for each lot to undergo one day of process time, at the defined speed (x-factor), in each day (24 hours).
In a range management system, each range has a daily takt rate (DTR) which is the ideal daily throughput rate for that range. Takt is a German word for “beat” and represents the pace at which product moves through the manufacturing process. Daily targets for each range are set based on the DTR and also the knowledge of how much WIP is in the range, and how much WIP is in the next range. The objective is to keep WIP balanced, while achieving one day of process time on each lot. When a range meets the target output for a day, the range is stopped so that effort can be placed on other lots in ranges that still need to achieve the target output. When a lot gets behind schedule and does not complete the one day of process time, a gap may exist in the WIP profile, and an acceleration mode, or pull factor, may be applied to accelerate WIP to fill the gap. By operating the manufacturing line with this methodology, the WIP stays balanced and resources are evenly distributed to process WIP across all operations in the manufacturing line.
Standard range management systems work well with production WIP that is on a predefined and stable route in which its flow and total process cycle time is predictable. However, WIP does not always follow a predefined route. For instance, the flow of some new technology WIP may vary from the predefined routes depending on the experimentation required of the product. The total cycle time of any given lot of new technology WIP is not predictable because it is unknown which operations the lot may undergo.
Trying to control new technology WIP with daily takt rates and rules based on range definition does not work well. A further problem arises when a fabricator shares resources and machines between a mix of production WIP and new technology WIP. The disparate nature of the different types of WIP makes it difficult to treat them equivalently from an x-factor point of view. As a result, it is difficult to manage the manufacturing of production WIP and new technology WIP within the same fabrication system.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.